A hybrid vehicle, an electric vehicle, a note-type personal computer and other devices use assembled batteries. The assembled battery is formed of a plurality of secondary batteries (battery cells) connected in series. It is necessary in such an assembled battery to detect individually a voltage of each battery cell for calculation of capacity of each battery cell and protective management.
A conventional device of this kind (for example, JP-A-2008-145180 corresponding to US 2008/0150516 A1) is formed of an A/D converter and a level shift circuit, which selects either one of battery cells and shifts an inter-terminal voltage of a selected battery cell to be within an input voltage range of the A/D converter.
The level shift circuit is generally formed of an integration circuit, which uses an operational amplifier and a capacitor. Among various types of A/D converters, a cyclic type A/D converter is most suited for size reduction. This cyclic type A/D converter A/D-converts an analog voltage, which is a conversion subject voltage to be converted, by an A/D converter of less number of bits, generates an analog voltage based on an A/D conversion result, generates a residual voltage by subtracting a generated analog voltage from the conversion subject voltage, amplifies the residual voltage and A/D-converts an amplified residual voltage by the A/D converter. A circuit for generating the residual voltage is formed of an integration circuit, which uses an operational amplifier and a capacitor.
Since both circuits include the operational amplifiers, which occupy large circuit areas and consume large electric power, as described above, the circuit area and power consumption of the entire device increases.